The present invention relates to plastic fasteners.
Plastic fasteners of the type commonly used, for example, to attach merchandise tags to articles of commerce, such as articles of clothing, are well known and are widely used in the retail industry. Typically, such fasteners comprise an elongated member having a first end shaped to define a cross-bar (also commonly referred to as a "T-bar"), a second end and a thin filament portion interconnecting the cross-bar and the second end. In use, the cross-bar is inserted first through a tag and then through a desired piece of fabric. The second end is appropriately sized and shaped to keep the tag from being pulled off the filament portion.
Typically, such fasteners are mass-produced into one of two different forms known as fastener stock. One type of fastener stock comprises a plurality of fasteners joined together at their respective cross-bars by an orthogonally disposed runner bar. The other type of fastener stock comprises a plurality of fasteners arranged in an end-to-end alignment, the ends of successive fasteners being joined together by severable connectors so as to form a length of continuously connected fastener stock.
The dispensing of individual fasteners from fastener stock into desired articles of commerce is typically accomplished using an apparatus commonly referred to as a tagger gun. Typically, a tagger gun includes (a) a hollow needle having a longitudinal slot extending across its length; (b) means for separating an individual cross-bar from the remainder of the fastener stock; and (c) means for feeding the individual cross-bar through the hollow, slotted needle and the desired article of commerce. Connections, if any, between the ends of adjacent fasteners are severed by pulling the tagger gun away from the article of commerce after the cross-bar of one of the fasteners has been inserted thereinto.
Fastener stock is commonly mass-produced through a process of continuous molding. In U.S. Pat. No. 4,461,738 to Russell, there is disclosed a method of continuous extrusion molding of objects using a rotatable molding wheel with peripheral orifices in accordance with the objects to be molded. Plastic is extruded upon the periphery of the wheel and a knife in substantially elliptical contact is used to skive film from the objects being molded.
Typically, the process of continuous molding is capable of producing only a length of fastener stock in which each individual fastener includes a filament of reduced length and increased thickness. As a result, upon completion of the molding process, selected portions of the fasteners in the fastener stock are often subjected to a stretching process. The process of stretching fastener stock is well known in the art and is commonly used to produce fastener stock in which each individual fastener includes a filament of increased length and reduced thickness. Often the stretching process is performed using a pair of diverging sprocket wheels which rotate to stretch the filamentary portions.
It is desirable for plastic fasteners of the type described above to be manufactured in such a manner so as to have a high tensile strength. Plastic fasteners, and in particular the thin filament of plastic fasteners, require a high tensile strength for numerous reasons. For instance, plastic fasteners of the type described above must be manufactured in such a manner so as to be strong enough to prevent unscrupulous shoppers from severing the thin filament which, in turn, can enable the shopper to remove the fastener and price tag from the article of commerce without paying. Furthermore, plastic fasteners of the type described above must be manufactured in such a manner so as to be strong enough to withstand the force of the stretching process. For example, plastic fasteners of the type commonly used for shoe-lasting applications, such as U.S. Pat. No. 5,586,353 to Merser, can require approximately 50 pounds of force to stretch the molded fastener into the finished product. Oftentimes, this amount of stretching force can exceed the tensile strength of the fastener and, as a consequence, cause the filament to sever during the stretching process.
Numerous techniques have been used to increase the tensile strength of the thin filament of plastic fasteners.
One technique employed to increase the tensile strength of fasteners is accomplished by molding the fastener stock using an inherently strong plastic material, such as nylon, instead of using an inherently weaker plastic material, such as polypropelene or polyeurethane.
One drawback of molding fasteners out of a stronger plastic, such as nylon, instead of a weaker plastic, such as polypropelene or polyeurethane, is that the stronger plastics are typically more expensive than the weaker plastics. For example, the cost of nylon is approximately twice as expensive as the cost of polypropelene and polyeurethane.
Another technique used to increase the tensile strength of fasteners is accomplished by increasing the thickness of the thin filament. It should be noted that the thickness of the cross-bar of the fastener can not be similarly increased because an increase in the cross-sectional size of the cross-bar may preclude the fastener from being able to fit within the hollow needle of conventional tagger guns.
There are numerous drawbacks which result from increasing the thickness of the thin filament.
One drawback which results from increasing the thickness of the filament is that the plastic fastener often will sever or become distorted during the stretching process. Specifically, because the thickness of the filament is increased without increasing the thickness of the cross-bar, there is exists a considerable difference in the tensile strength between the cross-bar and the filament. Furthermore, because the thickness of the filament is increased, a larger amount of force is required to stretch the filament during the stretching process, an amount of force which the weaker cross-bar is unable to withstand. As a consequence, the junction of the cross-bar and the filament may sever or become improperly distorted, the improper distortion of a stretched fastener often being referred to as necking in the art. The distortion of a fastener is significant in that the fastener may no longer be shaped so as to be able to fit through the slot of the needle of standard tagger guns.
Another drawback which results from increasing the thickness of the filament is that the thicker fastener will create a larger hole in the article of clothing being tagged. Specifically, during the tagging process of an article of clothing, a tagger gun bends the cross-bar of the fastener in a near parallel relation to the thin filament. The bending process decreases the size of the hole in the article of clothing through which the fastener needs to pass. However, because the thickness of the filament is increased for the thicker fastener, the cross-bar is not able to be bent in a near parallel relation to the filament. As a consequence, the size of the hole in the article of clothing being tagged is increased, which is undesirable.